Microsoft co-founder Bill Gates has admitted that making users press Ctrl, Alt, Delete to log on to PCs was a "mistake".

The familiar three-fingered command is used without much thought by tens of millions of people to log on to work and home machines.

It also allows users to access task manager, or lock their PCs from prying eyes.

Speaking during an interview at Harvard University, Mr Gates was asked why logging on to a machine could not be simpler and admitted that, in hindsight, it was the wrong choice.

"We could have had a single button but the guy who did the IBM keyboard design didn't want to give us our single button - it was a mistake," he said, prompting applause and laughter from the audience.

Millions face a familiar routine to log on to their computers each day

The Ctrl, Alt, Delete command was actually the brainchild of David Bradley, one of the computer engineers who worked on the original IBM PC.

He previously said it took him minutes to come up with the combination and chose it because it is difficult to press the keys accidentally.

It was originally only supposed to be a tool for programmers to reboot their computers, but gradually filtered through to the public and became commonplace.

Speaking in 2001, Bradley said he had no idea he was creating a "cultural icon".

"I have to share the credit," he said. "I may have invented it but I think Bill (Gates) made it famous."

Mr Gates, the world's second richest man with an estimated $67bn (£42bn), stepped down as Microsoft boss in July 2008 and now devotes much of his time to the charitable foundation he runs with his wife.